A fire truck drives past a home destroyed by the Fourmile Canyon Fire west of Boulder, Colorado, on September 11, 2010. For a description of the burn patterns and building construction on the Fourmile Canyon Fire, see "Tour of the Fourmile Canyon Fire: Questions Raised, Answers Pending," a blog posting from June 27, 2011, on NFPA’s Firewise website, firewise.org.

Large-Loss Fires in the United States in 2010The $217 million Fourmile Canyon Fire tops the list of last year’s costliest fires in terms of property loss

On September 6, 2010, the situation in Fourmile Canyon, Colorado, was ripe for a wildland fire. Humidity was a low 7 percent, the winds were from the west-southwest at 12 to 15 mph (19 to 24 kph), and only 1.3 inches (3.3 centimeters) of rain had fallen in more than a month. It was a red flag day, meaning that critical fire weather conditions were present, or shortly would be.

The call came into the fire department at about 10 a.m. Winds had reignited a fire set in a fire pit several days prior, and embers blowing out of the pit ignited what was to become a $217 million wildfire, the largest wildfire in terms of dollar loss in Colorado’s history.

Driven by the wind, the fire’s surface flames grew 20 to 50 feet (6 to 15 meters) high and started a running crown fire, burning the Ponderosa pine and native shrubs covering the south-facing slopes of the canyon and the Douglas fir on the north-facing slopes. Aspen, grasses, mountain mahogany, cottonwood, mountain maple, river birch, and common riparian vegetation also grew in the canyon.

Fifty firefighters responded within two hours of the initial call, and 34 fire agencies responded during the next 48 hours. Over the next week, they fought the blaze with retardant-dropping aircraft, helicopters, bulldozers, fire engines, and water tenders as the fire burned through steep, heavily forested canyons, destroying outbuildings and homes. By the end of the week, more than 1,100 firefighters had responded to the scene.

The fire was finally contained on September 13, after burning 6,179 acres (2,501 hectares) and destroying 172 structures. Of those structures, 166 were homes. Another 26 homes were damaged, and suppression costs totaled almost $10 million. Fortunately, there were no fatalities and only seven minor injuries to firefighters.

The Fourmile Canyon Fire was one of 17 large-loss fires that occurred in the United States last year. Large-loss fires and explosions are defined as incidents that cause at least $10 million in direct property loss. Each year, NFPA reports on the previous year’s large-loss fires, tracking and verifying loss information reported in the media or by other sources. The 17 large-loss fires of 2010 are only those fires for which we obtained an official dollar loss. Several fires we tracked might have resulted in losses of more than $10 million, but we could not verify through an official source the size of the loss or information about the incident.

According to “Fire Loss in the United States During 2010” [September/October], U.S. fire departments responded to an estimated 1,331,500 fires in 2010 that caused an estimated loss of $11.6 billion. Of these, 482,000 were structure fires and 849,500 were non-structure fires. Many of these fires were small or resulted in little or no reported property damage. However, the 17 that resulted in losses greater than $10 million each caused a total of roughly $950 million in direct property losses. Although these fires accounted for only 0.001 percent of the estimated number of fires in 2010, they accounted for 5.6 percent of the total estimated dollar loss.

Over the past 10 years, the number of large-loss fires annually has ranged from 16 to 45, with an average of approximately 24 per year. When adjusted for inflation to 2001 dollars, the number of fires in 2010 that could be categorized as large-loss fires drops to 10, with an adjusted loss of $479 million in 2001 dollars.

In 2010, the costliest seven fires did more than $20 million each in property damage. These seven fires, which include five structure fires, the Fourmile Canyon Fire, and an outside explosion and fire, resulted in a combined property loss of $532.5 million, which represents 56 percent of the total loss in large-loss fires and 4.6 percent of the total fire losses of 2010. The Fourmile Canyon Fire and a shopping mall fire were the two largest, doing a combined $327 million in damage.

Where fires occurredFifteen of the 17 large-loss fires of 2010 occurred in structures, resulting in a total property loss of $369.8 million. Only two, the Fourmile Canyon Fire and an outside natural gas explosion and fire, occurred outside structures, resulting in losses of $217 and $65 million, respectively.

Of the 15 structure fires, four occurred in public assembly properties — two in churches, one in a restaurant, and one in a clubhouse—and resulted in a loss of $50 million. Three fires, which did $70 million in damage, occurred in storage properties. One was a warehouse containing electronic equipment, another was a produce storage facility, and the third was a paper records storage warehouse.

Another two fires occurred in schools, one a middle school and the other an elementary school. Two fires also occurred in manufacturing properties, a sawmill and a metal products plant. These four fires resulted in total losses of $65.8 million.
A fire in a shopping mall, a wastewater treatment plant, a building being renovated, and a single-family home resulted in losses of $110 million, $52 million, $12 million, and $10 million respectively.

Information on the operating status was reported for nine of the 15 structure fires. When the fires broke out, three were at full operation or occupancy and six were closed.

Information on the cause of 10 of the structure fires was also reported. Five were deliberately set, resulting in a loss of $173.5 million, or 26.6 percent of the fire loss in large-loss fires. Other causes included a mechanical failure in a rooftop air-conditioning unit, a light bulb installed too close to combustible items, spontaneous heating of agricultural products, and a rekindle of a previous fire.

Six of the fires, all in structures, broke out between 11 p.m. and 7 a.m.

Detection and suppression systemsInformation about detection equipment was reported for eight of the 15 structure fires. Three of the fires occurred in properties that had no automatic detection equipment. Of the other five structures, two had complete coverage smoke alarms, two had smoke alarms with unreported coverage, and one had a detection system of an unreported type. Three of the five systems operated effectively, while the operation or effectiveness of the other two systems was not reported.

Information about automatic suppression equipment was reported for nine of the 15 structure fires. Four had no suppression equipment. Of the remaining five, four had wet-pipe sprinklers; one provided complete coverage, one provided partial coverage, and the coverage of the other two was not reported. The fifth structure had a dry-pipe system of unreported coverage.

Three of the five suppression systems operated, and two did not. Of the systems that operated, two were effective and helped control the fire; one was not in the area of ignition, but it controlled the spread of the fire. The third system that operated was shut down prematurely during the fire for unreported reasons. The two systems that failed to operate had been shut down before the fires started.

Complete information on both detection and suppression equipment was reported for eight of the 15 large-loss structure fires. Both systems were present in three structures. Two structures had only detection equipment, and two had only suppression equipment. In one fire, the structure had neither detection nor suppression systems.

What we can learnThis study reports on the small share of fires that account for major losses. There were eight fewer large-loss fires in 2010 than there were in 2009, and associated property losses decreased by more than $298.4 million, or 31 percent. In seven of the past 10 years, at least one fire has resulted in a loss of more than $100 million, and in at least three years, there was one loss of more than $1 billion. In 2010, two fires did more than $100 million in damage, for a total property loss of $327 million.

Adhering to the fire protection principles reflected in NFPA’s codes and standards is essential if we are to reduce the occurrence of large-loss fires and explosions in the United States. Proper construction, storage, and housekeeping will make fires less likely to occur and help control or limit the fire spread should a fire occur, while proper design, maintenance, and operation of fire protection systems and features can keep a fire that does occur from becoming a large-loss fire.

AcknowledgementsNFPA would like to thank the U.S. fire service for its contributions of data, without which this report would not be possible. In one case, the fire department was unable to contribute complete details to NFPA because legal action is pending or ongoing. The author also wishes to thank Norma Candeloro and the staff of the Fire Analysis Department for providing the support this study requires.

Where we get our dataNFPA identifies potential large-loss incidents by reviewing national and local news media, including fire service publications. A clipping service reads all U.S. daily newspapers and notifies NFPA’s Fire Analysis and Research Division of major large-loss fires. NFPA’s annual survey of the U.S. fire experience is an additional data source, although not the principal one.

Once an incident has been identified, we request information about the fire from the fire department or agency having jurisdiction. We also contact federal agencies that have participated in investigations, state fire marshals’ offices, and military sources. The diversity and redundancy of these data sources enable NFPA to collect the most complete data available on large-loss fires.

Stephen G. Badger is a fire data assistant in NFPA’s Fire Analysis and Research Division and is retired from the Quincy, Massachusetts, Fire Department.